Known from the prior art are different processes and apparatuses for manufacturing composite materials from mainly solid raw stock. The raw stock and optional additives may be conducted directly to an extrusion process or to an extrusion process via a preliminary treatment process, e.g. granulation or a mixing process, to manufacture the composite material.
Furthermore, it is known from the prior art, e.g. from reference US 2004/0126515, to add a coupling agent to raw stock in the manufacture of composite material, especially wood composite material, at the extrusion stage. It is known to use maleic anhydride modified polyolefins, e.g. MAPE and MAPP, as the coupling agent in the manufacture of wood composites. MAPE or MAPP reacts with wood fibers, forming a covalent bond between the carbonyl group of the anhydride and the hydroxyl group of the fiber. The polyolefin moiety of the coupling agent binds mechanically to the polymeric matrix of the raw stock. Also silane based coupling agents are used. A high process temperature, mainly of above 180° C., is needed at the stage where the coupling agent is added, so that sufficient adhesion is acquired between the coupling agent and raw stock. Providing a sufficiently high process temperature without a separate heating stage is often problematic. Another problem has been to provide sufficiently good adhesion between lignin-free fiber and plastic. Before, a sufficiently strong bond has not been provided between lignin-free fiber and plastic in the presence of a coupling agent. In this case, the mechanical properties of the composite material to be formed have been poor.